Hearing devices are portable hearing apparatuses which are used to supply the hard-of-hearing. To accommodate the numerous individual requirements, different configurations of hearing devices such as behind-the-ear hearing devices (BTE), in-the-ear hearing devices (ITE), e.g. including conch hearing devices or channel hearing devices (CIC), are provided. The hearing devices given here as examples are worn on the outer ear or in the auditory canal. Furthermore, bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The damaged hearing is stimulated either mechanically or electrically in such devices.
Essential components of the hearing devices include in principal an input converter, an amplifier and an output converter. The input converter is generally a receiving transducer, e.g. a microphone and/or an electromagnetic receiver, e.g. an induction coil. The output converter is mostly realized as an electroacoustic converter, e.g. a miniature loudspeaker, or as an electromechanical converter, e.g. a bone conduction receiver. The amplifier is usually integrated into a signal processing unit. This basic configuration is shown in the example in FIG. 1 of a behind-the-ear hearing device. One or more microphones 2 for recording the ambient sound are incorporated in a hearing device housing 1 to be worn behind the ear. A signal processing unit 3, which is similarly integrated into the hearing device housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker and/or receiver 4, which outputs an acoustic signal. The sound is optionally transmitted to the ear drum of the device wearer via a sound tube, which is fixed with an otoplastic in the auditory canal. The power supply of the hearing device and in particular of the signal processing unit 3 is provided by a battery 5 which is likewise integrated into the hearing device housing 1.
The power of a transmitter in a data transmission system must be configured such that a level which is sufficient for demodulating the signal reaches the receiver even in the case of a maximum admissible distance between the transmitter and receiver. In this way, the attenuation of the signal, the interference and external faults are taken into consideration. The attenuation is very heavily dependent on the distance between the transmitter and receiver, so that under some circumstances a significantly stronger signal level reaches the receiver with shorter transmission distances than would be necessary for transmission purposes. This can lead to overloading and non-linear distortions in the receiver and to unnecessary energy consumption in the transmitter. Excessively high distortions can render the transmission completely impossible in the case of very short distances. Furthermore, in extreme cases, a very high reception level can damage the receiver. This behavior is particularly pronounced in the case of inductive transmission systems, such as in hearing devices and hearing device accessories, because the dependency of the signal attenuation on the distance is greater here than in the case of electromagnetic systems (e.g. Bluetooth, cellular radio).
With hearing devices, the unnecessary energy consumption during transmission was previously often accepted. On the receiver side, an automatic gain control (AGC) is mostly implemented, which reduces overloading and distortions. Also known from the cellular radio field is increasing the transmission power with poor availability, which is equivalent to reducing the transmission power with good availability (see EBERSPÄCHER, J.; VÖGEL, H.-J.: GSM Global System for Mobile Communication. Stuttgart: Teubner, 1997, pages 100-111. ISBN 3-519-06192-9).
The publication DE 102005005603 A1 discloses a data transmission apparatus for wireless data transmission for hearing devices and a corresponding method. So that hearing devices can be reached over longer transmission paths, a converter unit with a high frequency receiving device for receiving high-frequency signals of an external transmitting unit is proposed. The converter unit also has a mixer unit for mixing the high-frequency signal with a reference signal, so that an output signal can be generated, the frequency of which is lower by at least one order of magnitude and which is suited to inductive transmission. The output signal is then transmitted inductively from the converter to the hearing device.